Contagion Theory and Contagion Practice in Fifteenth-Century Milan*

Abstract

When used to understand and combat the spread of bubonic plague, "contagion" is not a very helpful term. Plague is ecologically a complex disease transmitted from rodents to humans via fleas, and human-to-human passage of the disease is uncommon. Moreover, humans do not form lasting immunity to plague and cannot maintain the microorganism in human populations in the absence of infected rodents and their fleas. There can be no "Typhoid Mary" figure in the passage of plague.